Conventionally, chairs with folding seats comprise at least an underframe which has a roughly longitudinal axis and to which a backrest may be fixed, and with respect to which a horizontal axle is determined, the seat comprising a first part projecting forwards with respect to the horizontal axle and essentially intended to accommodate the seated user, and a second part projecting towards the underframe.
As is known, a folding seat has to fold itself back up when the chair is not in use and must essentially do this and do this in a way which does not deteriorate over time in order to remain compliant with the rules and regulations governing the fitting-out of halls that receive the public and, in particular, to comply with safety standards.
The folding seat must effect an automatic angular rotation of the order of 80 to 110 degrees about the aforementioned horizontal axle when the chair thus equipped is not in use, so as to adopt a roughly vertical position.
To this end, either the second part of the seat is provided with a counterweight, so as to overcome the forces of gravity generated by the first part, or a spring is added, for example a flat spiral spring on the horizontal axle, or a coil spring connecting one of the parts of the seat to the underframe, or alternatively a metal-leaf spring operated by an off-centre shaft, so that the spring is stressed when the seat is deployed and restores the stored energy to close the seat again when the user stands up.
In all cases, a set of elastic stops, for example made of rubber, are provided to slow and halt the angular rotational movement of the seat at the end of its travel. This set of stops necessarily leads to the chair having an increased thickness in the region of the closure mechanism, which results in the seat remaining partially deployed and therefore in the chair occupying additional space when the seat is up.
The raising of the seat through inertia in any case remains lacklustre and carries the risk of not being effected correctly as a result of simple unforeseen friction of the set or friction at the rotational axle.
The various spring-loaded seat-lifting means are, for their part, subject to mechanical fatigue because the spring remains under tension when the seat is deployed when the chair is in the position of use. This then results in relatively short durability of, and significant maintenance on, each chair to regularly change the spring-loading means.
Obviously, such means also result in a substantial acceleration of the angular movement of the seat, which then strikes the end-of-travel stops at full angular speed. The seat therefore, at the end of its travel, bangs against the stops provided for this purpose, and this gives rise to a banging noise which is unacceptable when, for example, in a lecture theatre so equipped, the lecturer has not finished giving his lecture or the show is still going on.
Furthermore, the fact that the seat reaches the elastic stops at high angular speed leads to significant stop wear, and these stops therefore constitute wearing parts which have to be changed regularly to make sure that they exhibit roughly constant characteristics.
Furthermore, the amount by which each seat remains slightly deployed in the up position also depends on the stop wear and therefore on the use of each chair. This results in residual deployment which differs from one chair to another, and soon results in misalignment of the raised seats of one and the same row of chairs. This is unattractive and may lead to problems regarding compliance with safety standards determining the required width of the passageway between the chair with the seat up and the work surface or chair facing it.
Furthermore, as has just been stated, these chairs are subject to a certain number of very tight regulations, because they are used in places that receive the public and, among these tight regulations, the durability factor is very important. The durability factor should be understood as meaning the number of deployment-closure cycles that can be performed before there is an appreciable degradation in the residual amount by which the seat remains deployed. Thus, it is known that a chair equipped with a spring-loaded seat-lifting means is generally not able to withstand more than about 40 000 cycles before the seat-lifting means requires maintenance or changing.
Document U.S. Pat. No. 3,594,037 describes a chair for an air stewardess comprising an operating strut, but in which the seat moves from the vertical to the horizontal position and vice versa about an essentially mobile and non-concrete axis of rotation. The backrest accompanies the seat in its movement and is therefore not fixed. The chair is referenced with respect to the ground, because the problem of tiers at different heights, as in a lecture theatre, does not arise in an aeroplane.
The invention falls within this context and its prime object is to obviate the aforementioned drawbacks while at the same time complying with the regulations in force.
Another object of the invention is to appreciably increase the durability factor, that is to say the number of seat deployment-closure cycles that can be effected without degradation, so as to reduce the need for chair maintenance.
Another object of the invention is to remove the need for a set of stops equipping each chair so as to avoid any additional residual deployment due to the wear of these stops.